Laying of sewers


The centre line of a sewer is indicated on the roads and streets according to the designs, moving upward from the lowest point or outfall of the main. Chain and a theodolite or compass is used to lay out the work. In order to check the centre line during construction, wooden pegs or steel spikes are typically driven at intervals of 10 metres on a line parallel to the centre where installing sewers won’t disturb them. Temporary benchmarks are set up at 200–400 metre intervals to monitor the levels and alignment of sewer lines. These benchmarks’ reduced level (R.L.) should be determined in relation to G.T.S benchmarks. Sewer appurtenance positions are also shown on the centre line.


The first phase is the removal of pavement, which begins at the lower end of the sewers and moves upward after noting the arrangement of the sewer lines on the ground. Concrete pavement removal tools include pickaxes, spades, and pneumatic drills. Trench digging is done either manually or with the use of machinery after pavement removal. The sewer line’s diameter and depth below ground determine the trench’s width.

For ease of lowering and altering the sewer pipe, the sewer line’s breadth is 15 cm wider than its exterior diameter. Even extremely tiny size sewers can be laid and joined conveniently with a minimum trench width of 60 to 100 cm. The need for trench side excavation require shoring and shuttering and also dewatering is done by gravity method or pumping method.


In order for sewage to exclusively flow into sewers owing to gravitational flow, trenches are dug with the right grade. Sewers’ centre line and grades are transferred from the using a boning rod and a sight rail, the ground. If a sewer needs to be installed in a soil, the trench must be dug deeper than what is necessary, whether it is in reclaimed land or subsurface strata. Typically requires rock or trench bottom. When the soil is really poor, the trench bottom should be filled in with grade-appropriate cement concrete. Where there is a risk of subsidence. The pipe sewer must be installed on a pile- or platform-supported concrete cradle or platform made of wood. In the case of casting-site sewers and R.C.C section with reinforcement, bearing capacity is encountered and soil stabilization shall be done either by rubber, concrete or wooden crib.


Only the pipe layers themselves can directly lay smaller pipes by hand. However, thicker and heavier pipes are dropped into the trenches by being roped around and supported through the hock. To make joining easier, it is customary to lay pipes with upgraded socket ends. After carefully positioning and arranging the pipes, they are linked by bringing them close and inserting the spigot end of one pipe into the socketed end of the other. Carefully curing the joints for an appropriate amount of time


The C.I Pipes must be checked for line and level, and any empty space in the socket must be filled with molten piglead of the highest quality in accordance with IS:782 and IS 3114. For concrete pipes, the collars must be symmetrically positioned over the ends of the pipes. The annual space between the inside of the collar and the outside of the pipe must be filled with hemp yarn soaked in tar or cement slurry that has been thoroughly packed and rammed with caulking tools before being filled with cement mortar 1:2. The joints must be completed with a fillet that slopes at 45 degrees to the pipe’s surface and is cured for 24 hours.

For stoneware pipes, each connection must be caulked with tarred gasket that is one length for each joint and long enough to completely round the pipe’s spigot end. The seal shall then be partially dried, filled with a 1:2 cement sand mortar, and a fillet shall be applied made a 45° angle with the pipe’s barrel around the seam using a trowel per IS 4217. For jointing, rubber gasket can also be employed.

Shubhajna Rai
Shubhajna Rai

A Civil Engineering Graduate interested to share valuable information with the aspirants.

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